Adrenal medulla hormones

ADRENAL MEDULLA HORMONES. Adrenaline (epinephrine) and its immediate biological precursor noradrenaline (norepinephrine, levartei-nol) are the principal hormones of the adult adrenal medulla. See Fig.l. Some of the physiological effects produced by adrenaline arc contraction of the dilator muscle of the pupil of the eye (mydriasis), relaxation of the smooth muscle of the bronchi constriction of most small blood vessels dilation of some blood vessels, notably those in skeletal muscle increase in heart rate and force of ventricular conlraction relaxation of the smooth muscle of the intestinal tract and either contraction or relaxation, or both, of uterine smooth muscle. Electrical stimulation of appropriate sympathetic (adrenergic) nerves can produce all the aforementioned effects with exception of vasodilation in skeletal muscle. 

Use of Hormones in Nonendocrine Disease. There are many examples of how various hormones and hormone-related drugs can be used to treat conditions that are not directly related to the endocrine system. For instance, certain forms of cancer respond to treatment with glucocorticoids (see Chapter 36). Drugs that block the cardiac beta-1 receptors may help control angina and hypertension by preventing excessive stimulation from adrenal medulla hormones (epinephrine, norepinephrine see Chapters 21 and 22). 

In the anterior pituitary gland (see Hormones, anteriorpituitaryhormones), both adrenocorticotropic hormones (ACTH) and the endogenous opiate hormone, P-endorphin, are synthesized from a common prohormone (2) (see Opioids,endogenous). In the adrenal medulla, five to seven copies of another opiate hormone, methionine—enkephalin (Met-enkephalin), and one copy of leucine—enkephalin (Leu-enkephalin) are synthesized from each precursor molecule (3). 

PNMT catalyzes the N-methylation of norepinephrine to form epinephrine in the epinephrine-forming cells of the adrenal medulla. Since PNMT is soluble, it is assumed that norepinephrine-to-epinephrine conversion occurs in the cytoplasm. The synthesis of PNMT is induced by glucocorticoid hormones that reach the medulla via the intra-adrenal portal system. This special system provides for a 100-fold steroid concentration gradient over systemic arterial blood, and this high intra-adrenal concentration appears to be necessary for the induction of PNMT. 

The adrenal gland is located on the upper segment of the kidney (Fig. 42-1). It consists of an outer cortex and an inner medulla. The adrenal medulla secretes the catecholamines epinephrine (also called adrenaline) and norepineprhine (also called noradrenaline), which are involved in regulation of the sympathetic nervous system. The adrenal cortex consists of three histologically distinct zones zona glomerulosa, zona fasciculata, and an innermost layer called the zona reticularis. Each zone is responsible for production of different hormones (Fig. 42-2). 

The endogenous release of the potent vasoconstrictor neuropeptide Y (NPY) is increased during sepsis and the highest levels are detected in patients with shock (A8). NPY is a 36-amino-acid peptide belonging to the pancreatic polypeptide family of neuroendocrine peptides (T2). It is one of the most abundant peptides present in the brain and is widely expressed by neurons in the central and peripheral nervous systems as well as the adrenal medulla (A3). NPY coexists with norepinephrine in peripheral sympathetic nerves and is released together with norepinephrine (LI9, W14). NPY causes direct vasoconstriction of cerebral, coronary, and mesenteric arteries and also potentiates norepinephrine-induced vasoconstriction in these arterial beds (T8). It appears that vasoconstriction caused by NPY does not counterbalance the vasodilatator effects of substance P in patients with sepsis. The properties of vasodilatation and smooth muscle contraction of substance P are well known (14), but because of the morphological distribution and the neuroendocrine effects a possible stress hormone function for substance P was also advocated (J7). Substance P, which is a potent vasodilatator agent and has an innervation pathway similar to that of NPY, shows a low plasma concentration in septic patients with and without shock (A8). 

As previously mentioned, the cells of the adrenal medulla are considered modified sympathetic postganglionic neurons. Instead of a neurotransmitter, these cells release hormones into the blood. Approximately 20% of the hormonal output of the adrenal medulla is norepinephrine. The remaining 80% is epinephrine (EPI). Unlike true postganglionic neurons in the sympathetic system, the adrenal medulla contains an enzyme that methylates norepinephrine to form epinephrine. The synthesis of epinephrine, also known as adrenalin, is enhanced under conditions of stress. These two hormones released by the adrenal medulla are collectively referred to as the catecholamines. 

Adrenal medulla. Derived from neural crest tissue, the adrenal medulla forms the inner portion of the adrenal gland. It is the site of production of the catecholamines, epinephrine and norepinephrine, which serve as a circulating counterpart to the sympathetic neurotransmitter, norepinephrine, released directly from sympathetic neurons to the tissues. As such, the adrenal medulla and its hormonal products play an important role in the activity of the sympathetic nervous system. This is fully discussed in Chapter 9, which deals with the autonomic nervous system. 

The major circulating hormones that influence vascular smooth muscle tone are the catecholamines epinephrine and norepinephrine. These hormones are released from the adrenal medulla in response to sympathetic nervous stimulation. In humans, 80% of catecholamine secretion is epinephrine and 20% is norepinephrine. Stimulation of cy-adrenergic receptors causes vasoconstriction. The selective a,-adrenergic receptor antagonist, prazosin, is effective in management of hypertension because it causes arterial and venous smooth muscle to relax. 

Adrenal gland A triangle-shaped organ positioned at the top of the kidney which functions as a double endocrine gland . The larger outer adrenal cortex secretes three classes of steroid hormones glucocorticoids (e.g., cortisol), minerlocorticoids (aldosterone) and small amounts of sex steroids (e.g., testosterone). The inner adrenal medulla secretes catecholamines (e.g., adrenaline and noradrenaline). 

Epinephrine, a hormone made in the adrenal medulla and sympathetic nerve endings, calls for rapid mobilization of energy and glucose. Epinephrine, like glucagon, binds to specific cellular receptors and activates adenylate cyclase. For the most part, epinephrine can be considered... 

Li+ has been reported to affect virtually every component of the endocrine system to some extent however any resulting clinical manifestations are very rare [169]. Although these influences do not appear to be related to its mechanism of action in manic-depression, some are involved in the side effects experienced by Li+-treated patients. Apart from elevated levels of thyroid stimulating hormone (TSH), Li+ does not appear to affect the basal levels of hormones significantly however some hormone responses are reported to be altered by Li+ treatment of bipolar patients [170]. Neuronal activity stimulates the adrenal medulla to release norepinephrine and epinephrine into the blood and, consequently, the plasma from people with mania and depression shows increased levels of both neurotransmitters [171]. 

Histamine Hr Human cDNA Allergy inflammation, asthma, chronic sinusitis, rhinitis, epilepsy migraine, motion sickness, pain, cancer Smooth muscle contraction, increase in vascular permeability stimulation of hormone release (adrenal medulla), increase in neuronal firing... 

The adrenal medulla synthesizes two catecholamine hormones, adrenaline (epinephrine) and noradrenaline (norepinephrine) (Figure 1.8). The ultimate biosynthetic precursor of both is the amino acid tyrosine. Subsequent to their synthesis, these hormones are stored in intracellular vesicles, and are released via exocytosis upon stimulation of the producer cells by neurons of the sympathetic nervous system. The catecholamine hormones induce their characteristic biological effects by binding to one of two classes of receptors, the a- and )S-adrenergic receptors. These receptors respond differently (often oppositely) to the catecholamines. 

Adrenaline is the main hormone released from the adrenal medulla. The glandular cells in this structure correspond to the second, postganglionic neuron of the sympathetic nervous system. Furthermore, adrenaline can be found in chromaffin cells in various tissues. For the better understanding of the function of noradrenaline it is important to realize that this substance, as a neuronal transmitter, affects only the innervated target structure, that is it acts mainly locally. Among these effects are the activation of the musculus dilatator to widen the pupillae in response to a reduced light intensity, an increase in heart rate as a response to a blood pressure drop due to a reduction of the peripheral resistance or constriction... 

The cells of the adrenal medulla, called chromaffin cells, are homologous with sympathetic postganglionic neurons. The adrenal medulla may in fact be considered a modified sympathetic ganglion. The adrenal medulla secretes two hormones. One is norepinephrine, which is also the primary neurotransmitter of sympathetic postganglionic neurons. The other medullary hormone is epinephrine. 

General activation of the sympathetic system during stress, fear, or anxiety is accompanied by increased secretion of adrenal medullary hormones, which consist primarily of epinephrine in the human. The secretory activity of the adrenal medulla is regulated by the CNS. 

Hypothalamo-pituitary function Anterior pituitary hormones Posterior pituitary hormones Adrenal cortex Adrenal medulla Thyroid Pancreas INTRODUCTION... 

The ultimate effects of sympathetic stimulation are mediated by release of norepinephrine from nerve terminals, which then activates adrenoceptors on postsynaptic sites (see Chapter 6). Also, in response to a variety of stimuli such as stress, the adrenal medulla releases epinephrine, which is transported in the blood to target tissues. In other words, epinephrine acts as a hormone, whereas norepinephrine acts as a neurotransmitter. 

Table 9-4). Activation of 32 receptors in skeletal muscle contributes to increased blood flow during exercise. Under physiologic conditions, epinephrine functions largely as a hormone after release from the adrenal medulla into the blood, it acts on distant cells. Norepinephrine (levarterenol, noradrenaline) is an agonist at both 0 and tx2 receptors. Norepinephrine also activates receptors with similar potency as epinephrine, but has relatively little effect on 32 receptors. Consequently, norepinephrine increases peripheral resistance and both diastolic and systolic blood pressure. Compensatory baroreflex activation tends to overcome the direct positive chronotropic effects of norepinephrine however, the positive inotropic effects on the heart are maintained (Table 9-4). 

When an animal is confronted with a stressful situation that requires increased activity—fighting or fleeing, in the extreme case—neuronal signals from the brain trigger the release of epinephrine and norepinephrine from the adrenal medulla. Both hormones dilate the respiratory passages to facilitate the uptake of 02, increase the rate and strength of the heartbeat, and raise the blood pressure, thereby promoting the flow of 02 and fuels to the tissues (Table 23-6). 

The catecholamines are a group of hormones secreted by the adrenal medulla. The major urinary metabolite of norepinephrine and epinephrine is vanillylmandelic acid (VMA). Urinary levels of VMA are considerably higher than those of total catecholamine. From the standpoint of laboratory methodology, VMA estimation is preferable to total catecholamine estimation, although it is not a simple procedure. VMA has been shown to be elevated in some patients who had phenochromocytoma and normal urinary catecholamines, even though patients with neuroblastoma have a normal VMA level and elevated catecholamine levels. 

Adrenal Conical Hormones. The adrenal gland is made up of two parts, the medulla and the cortex, each of which secretes characteristic hormones. The hormones of the adrenal medulla art- the catecholamines, epinephrine adrenalin and norepinephrine (noradrenalint. which are closely related chemically, dil lning only in that epinephrine has an added methyl group. See Table I. In fact, animal experiments have established a metabolic pathway lor Ihe biosynthesis of both compounds Irom Ihe ammo acid pheny lal.inine. which involves enzy malic oxidation and decarboxylation reactions It is also to he noted ihui the isomeric form of norepinephrine is most important the natural D-lonn (which incidentally, is levorntatory) has many times die uciiviiy of die synthetic isomer. Epinephrine has a pronounced action upon the circulatory system, increasing both blood... 

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